black patterns on the sphere
Sculptris seems to mess a bit with custom split normals data (or the export routines at least). When Custom Normals are present, some functions of Blender won't give you the expected result (and recalculating the normals is one of them, as well as setting an Edge Split ange). Delete this data to free the normals again. You can do this in the Mesh Data tab using the Clear Custom Split Normals Data button:

After this, all normals are pointing in the same direction again:
before

after

finally, recalculate the normals using Ctrl + N: